The volume of the argument over climate change was turned up a notch at the end of November 2009, thanks to emails leaked from the Climatic Research Unit at the University of East Anglia. Shortly after the scandal broke I asked Trevor Davies, who was formerly a director of the CRU, and now has overall responsibility for research at the university, what it all meant. To start with, he told me: “There is no evidence that the research produced by CRU is flawed. On the contrary, it has been scrutinised and improved by the peer review process by which the global scientific community challenges and accepts new science. CRU’s research is consistent with other, independent, analyses, particularly two independent data sets in the US.”

As commentators locked horns, throwing up clouds of confusion, just a few of the hundreds of emails were the focus of the battle. Perhaps the most damning was a quote from the CRU’s Phil Jones in 1999, saying: “I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie, from 1981 onwards) and from 1961 for Keith’s to hide the decline.”

Researchers collect tree ring cores

The trick in question concerns tree rings. “This refers to a clever way of portraying in a diagram an analysis of, and compensation for, the breakdown in the strong relationship between tree-ring density and temperature in some parts of the world since the 1960s,” Davies told me. When compared to temperature data back as far as the middle ages and beyond, wood density increases have been directly proportional – until the second half of the 20th century. Jones himself contributed to a paper published in Nature – arguably the most difficult scientific journal to get published in – explaining this phenomenon nearly twelve years ago. So, charts using trees to measure temperatures over the whole century would need to use the “Nature trick”, taking into account how the link between wood density and temperature changed.

Critics have also focused on Jones’ suggestions that emails should be deleted to prevent them being accessed using freedom of information laws. These have been mentioned closely alongside criticisms that the raw data used by the CRU scientists had not been made available. Together, these give a particularly worrying sense that perhaps measurements have been destroyed to exaggerate the case for global warming. As mentioned in the last blog entry, the UK’s Met Office, a key collaborator with the CRU, has now released the raw data, to be met by fresh accusations of selective use of measurements. No definitive proof has yet come to light to support such claims, Davies points out. “There is no evidence that data have been lost, inappropriately adjusted or hidden,” he said.

Jones’ apparent efforts to try and suppress research criticising CRU research via the peer review process that Davies celebrates are at the centre of a third common criticism. Peer review, gathering and sharing of information and an investigation into suppression of data are all on the agenda of the independent review that the CRU has commissioned. “This demonstrates the commitment of the university to transparency and integrity in research,” Davies told me. “This is the correct way of responding to the orchestrated furore, rather than the many irresponsible distortions which have appeared in the blogosphere and some media. If the review concludes that there are issues to address, then address them we shall.”

Whatever the outcome of the review, Davies warns against discounting the majority view of the scientific community, on the basis of unsubstantiated allegations about what one part of it did. “The bigger picture is that the sum total of scientific evidence for global warming largely as a result of human activity is overwhelming,” he emphasised.